The major goals of this proposed research are to define the cis-acting sequences and trans-acting proteins required for the deployment of human immunodeficiency virus type 1 (HIV-1) as a gene-delivery vector. As part of this study we wish to thoroughly evaluate various aspects of HIV-1 vector design. The results of the proposed studies, we hope, will allow us to create, ultimately, a minimal HIV-1 p vector that is transduced efficiently into a wide variety of target cells (both growing and growth- arrested or quiescent); express the transgene at high levels or in a regulatable manner and reduce/eliminate the possibility of generating replication competent HIV-1 or novel replication competent recombinant retroviruses. The specific aims of this proposal are: 1) To define sequence requirements for creation of a minimal but efficient HIV-1 vector. 2) To further investigate the effect of co-expressing trans-acting accessory and regulatory proteins on gene transfer efficiency. 3) To develop second-generation HIV-1 vectors for enhanced transgene expression in transduced target cells.